1. Technical Field
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of achieving a good display quality, a high aperture ratio and a high display luminance even when a multi-gap layer (liquid crystal layer thickness-adjustment layer) formed of a transparent resin layer is provided on a color filter substrate.
2. Related Art
In recent years, as a liquid crystal display device used for portable apparatuses typified by cellular phones, a transflective type liquid crystal display devices employing both transmissive and reflective display modes has been widely used. The transflective type liquid crystal display device includes, within each pixel, a transmissive portion (transmissive region) having a transparent electrode and a reflective portion (reflective region) having a reflective layer. In a dark place, a backlight is turned on so that images are displayed using transmissive portions of individual pixels. On the other hand, in a bright place, images are displayed on reflective portions of the individual pixels using an external light without turning on the backlight. Therefore, since electronic apparatuses using the transflective type liquid crystal display device need not always turn on the backlight, an advantage can be obtained that the power consumption thereof can be reduced considerably.
The transflective type liquid crystal display device has an optical path difference between the reflective portion and the transmissive portion. This is because in the reflective display mode, light incident from the outside is emitted to the outside in a manner that it makes a round-trip in the liquid crystal panel, while in the transmissive display mode, light from an internal light source such as a backlight passes through the liquid crystal panel to be emitted to the outside. For the purpose of controlling the optical path difference, a method is generally performed in which a so-called multi-gap layer formed of a transparent resin layer is provided to the reflective portion of the transparent substrate so that an optical path in the reflective portion is adjusted by the multi-gap layer so that the length thereof becomes substantially equal to that of an optical path in the transmissive portion. In addition, in a general transmissive type liquid crystal display device, a multi-gap layer formed of a transparent resin layer is often formed in order to protect the color filter layer and improve the flatness.
However, when such a multi-gap layer is formed, a step is formed in a boundary region of the reflective portion in which the multi-gap layer exists and the transmissive portion in which the multi-gap layer does not exist. Moreover, when an electrode, a color filter layer, a multi-gap layer, a common electrode, a light shielding film, and the like are formed on a transparent substrate, and an material for alignment film is then applied by a roller, a surplus material for alignment film may remain close to a boundary of the step between the reflective portion and the transmissive portion due to the multi-gap layer, and thus, thickness unevenness of the alignment film may occur. Therefore, in JP-A-2006-267993, there is disclosed a transflective type liquid crystal display device in which a trench is formed in a multi-gap layer for each sub-pixel so as to extend along a signal line thereby to form a pathway for a surplus material for alignment film so that the congestion of the material for alignment film is suppressed.
A transflective type liquid crystal display device disclosed in JP-A-2006-267993 will be described with reference to FIGS. 9 to 11. In the drawings below used in this specification for explanation purposes, individual layers or individual members are appropriately depicted with different reduced scales in order to make them large enough to be recognized on the drawings but not necessarily proportional to the actual size thereof.
FIG. 9 is a cross-sectional view of the transflective type liquid crystal display device disclosed in JP-A-2006-267993 corresponding to one sub-pixel. FIG. 10 is a fragmentary plan view of a color filter substrate of the transflective type liquid crystal display device disclosed in JP-A-2006-267993. FIG. 11A is a cross-sectional view taken along the line XIA-XIA in FIG. 10. FIG. 11B is a cross-sectional view taken along the line XIB-XIB in FIG. 10.
The transflective type liquid crystal display device 10E includes an array substrate (substrate) AR and a color filter substrate CF. The array substrate AR includes an interlayer film 12, which is formed as necessary on a transparent substrate 11 such as a glass substrate, and a pixel electrode 13 formed thereon. A reflecting plate 14 is provided at the boundary of the interlayer film 12 on the left side of FIG. 9 and the pixel electrode 13, and this left portion corresponds to a reflective portion (reflective region) 15. Moreover, a portion on the right side of FIG. 9 where the reflecting plate 14 is not provided corresponds to a transmissive portion (transmissive region) 16. Further, an alignment film 17 is formed on a surface of the pixel electrode 13. In FIG. 9, a switching element, a gate insulating film, a passivation film, and the like are not illustrated.
A color filter substrate CF is disposed so as to face an array substrate AR having the pixel electrode 13, a gap between the array substrate AR and the color filter substrate CF is defined, for example, by a columnar rib (not illustrated), and liquid crystals LC are filled between the substrates. In the color filter substrate CF, as illustrated in FIG. 10, color filter layers 19 corresponding to three colors of F (red), G (green) and blue (B) arranged in a stripe form are arranged on a transparent substrate 18, such as a glass substrate, close to the array substrate AR. Moreover, on the color filter substrate CF, a multi-gap layer (also referred to as an overcoat layer) 20 formed of a transparent resin with a predetermined width is provided to the reflective portion 15 in order to adjust a cell gap between the reflective portion 15 and the transmissive portion 16.
The color filter layers 19 of the three colors R, C and B are formed with a predetermined gap 21e between them. The multi-gap layer 20 is formed to be located across adjacent ones of the reflective portions 15. Furthermore, since the color filter layers 19 of the three colors R, C and B form one pixel (one pixel), a trench 22e with a predetermined width is formed in the multi-gap layer 20 for each pixel in a width direction thereof so as to reach the transparent substrate 11. The trench 22e extends along the gap 21e of the adjacent color filter layers 19 and has a width larger than the gap 21e. In FIG. 10, the line denoted by a two-dot chain line is the outline of the multi-gap layer 20 when the trench 22e is not formed. Since the multi-gap layer 20 is formed with a resist according to a well-known photolithographic method, the trench 22e is formed at the same time with this. On the surfaces of the multi-gap layer 20 and the color filter layers 19, a common electrode 23 and an alignment film 24 are sequentially formed.
Then, liquid crystals LC are filled between the color filter substrate CF and the array substrate AR with the color filter substrate CF being disposed to face the array substrate AR, whereby a transflective type liquid crystal display device 10E disclosed in JP-A-2006-267993 is obtained.
According to the above-described transflective type liquid crystal display device 10E, although due to presence of the multi-gap layer 20, a step is formed at a boundary region of the reflective portion 15 and the transmissive portion 16, because when an material for alignment film is applied by a roller, a surplus material for alignment film may spread into the trench 22e, thickness unevenness of the alignment film 24 does not occur. However, since the alignment direction of liquid crystal molecules by the alignment film 24 in the X part (see FIG. 11A) of the inclined surfaces of the trench 22e is different from the alignment direction in the flat part of the multi-gap layer 20, the X part becomes an abnormal alignment region of liquid crystal molecules, which is called a disclination. Therefore, although this part of the trench 22e is shielded by the light shielding film 25 similar to the gap 21e between the adjacent color filter layers 19, since this part does not contribute to display, there is a problem that the aperture ratio of the liquid crystal display device decreases. Such a problem is particularly so because the step of the trench 22e may increase in the case of a display panel configured to perform color display in a transmissive display mode and monochromatic display in a reflective display mode and having no color filter layer on the reflective portion. As a result, the display quality may deteriorate greatly compared with the case of a display panel configured to perform color display in both transmissive display mode and reflective display mode.